The present invention relates to a disc brake assembly, and more particularly to an indicator system for disc brake air chamber overstroke.
Heavy-duty vehicles are typically equipped with a pneumatic brake actuating system. The brake actuating system applies air under pressure to a service chamber of a brake actuator. This moves a diaphragm and a push rod connected to a linkage which actuates the vehicle brakes. An emergency chamber having a power spring and a second diaphragm is often mounted on the service chamber. The emergency chamber drives the push rod and actuates the brakes to provide failsafe braking.
A brake actuator push rod has a predetermined amount of available movement or stroke. The amount of movement required to fully actuate the braking system of the vehicle is monitored to assure that it remains within the available stroke of the push rod. Excessive stroke of the push rod can result due to factors such as brake lining wear and loosening of mechanical linkages between the push rod and brake linkages. These factors may sometimes cause excessive push rod stroke, which is typically referred to as “overstroke.”
Various mechanical monitoring systems have been utilized to monitor push rod stroke during actuation of the brake and provide some indication to an operator when there is an overstroke occurrence. One known mechanical system includes a brightly colored ring painted on the push rod which indicates an overstroke condition when the ring extends out of the brake actuator during actuation of the brakes. The ring may, however, become difficult to see due to the location of the brake actuators and accumulated road debris. The common usage of automatic slack adjusters which incrementally adjust to compensate for slack in the braking system and to decrease the required push rod movement may further complicate such a system.
Various electronic monitoring systems utilizing sensors are also conventionally utilized. Disadvantageously, linkages utilized to actuate the sensor are often complicated and may be relatively fragile. The hostile environment in which the brake actuators are mounted may also damage the electronic systems, particularly where there are exposed components.
Accordingly, it is desirable to provide a brake overstroke indication system which is reliable, inexpensive and readily incorporated into a brake system having an automatic slack adjustment system.